Chronic social stress induces DNA methylation changes at an evolutionary conserved intergenic region in chromosome X

<p>Chronic stress resulting from prolonged exposure to negative life events increases the risk of mood and anxiety disorders. Although chronic stress can change gene expression relevant for behavior, molecular regulators of this change have not been fully determined. One process that could play a role is DNA methylation, an epigenetic process whereby a methyl group is added onto nucleotides, predominantly cytosine in the CpG context, and which can be induced by chronic stress. It is unknown to what extent chronic social defeat, a model of human social stress, influences DNA methylation patterns across the genome. Our study addressed this question by using a targeted-capture approach called Methyl-Seq to investigate DNA methylation patterns of the dentate gyrus at putative regulatory regions across the mouse genome from mice exposed to 14 days of social defeat. Findings were replicated in independent cohorts by bisulfite-pyrosequencing. Two differentially methylated regions (DMRs) were identified. One DMR was located at intron 9 of <i>Drosha</i>, and it showed reduced methylation in stressed mice. This observation replicated in one of two independent cohorts. A second DMR was identified at an intergenic region of chromosome X, and methylation in this region was increased in stressed mice. This methylation difference replicated in two independent cohorts and in Major Depressive Disorder (MDD) postmortem brains. These results highlight a region not previously known to be differentially methylated by chronic social defeat stress and which may be involved in MDD.</p

Targeted Sequencing of <i>FKBP5</i> in Suicide Attempters with Bipolar Disorder

<div><p>FKBP5 is a critical component of the Hypothalamic-Pituitary-Adrenal (HPA) axis, a system which regulates our response to stress. It forms part of a complex of chaperones, which inhibits binding of cortisol and glucocorticoid receptor translocation to the nucleus. Variations in both the HPA axis and <i>FKBP5</i> have been associated with suicidal behavior. We developed a systematic, targeted sequencing approach to investigate coding and regulatory regions in or near <i>FKBP5</i> in 476 bipolar disorder suicide attempters and 473 bipolar disorder non-attempters. Following stringent quality control checks, we performed single-variant, gene-level and haplotype tests on the resulting 481 variants. Secondary analyses investigated whether sex-specific variations in <i>FKBP5</i> increased the risk of attempted suicide. One variant, rs141713011, showed an excess of minor alleles in suicide attempters that was statistically significant following correction for multiple testing (Odds Ratio = 6.65, P-value = 7.5 x 10⁻⁴, Permuted P-value = 0.038). However, this result could not be replicated in an independent cohort (Odds Ratio = 0.90, P-value = 0.78). Three female-specific and four male-specific variants of nominal significance were also identified (P-value < 0.05). The gene-level and haplotype association tests did not produce any significant results. This comprehensive study of common and rare variants in <i>FKBP5</i> focused on both regulatory and coding regions in relation to attempted suicide. One rare variant remained significant following correction for multiple testing but could not be replicated. Further investigation is required in larger sample sets to fully elucidate the association of this variant with suicidal behavior.</p></div

Single-variant results with a P-value < 0.05.

<p>Single-variant results with a P-value < 0.05.</p

Sex-specific gene-level results using two minor allele thresholds.

<p>Sex-specific gene-level results using two minor allele thresholds.</p

Haplotype results generated using Haploview.

<p>Haplotype results generated using Haploview.</p

Schematic of the top variant in the <i>FKBP5</i> gene alongside previous findings.

<p>The top single variant result is displayed below the gene; variants or haplotypes with known associations to suicidal behavior are displayed above the gene. Gray variants were not covered by this study. Numbers represent references: <b>1.</b> [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0169158#pone.0169158.ref010" target="_blank">10</a>] <b>2.</b> [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0169158#pone.0169158.ref014" target="_blank">14</a>] <b>3.</b> [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0169158#pone.0169158.ref055" target="_blank">55</a>] <b>4.</b> [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0169158#pone.0169158.ref012" target="_blank">12</a>] <b>5.</b> [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0169158#pone.0169158.ref013" target="_blank">13</a>] <b>6.</b> [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0169158#pone.0169158.ref011" target="_blank">11</a>] <b>7.</b> [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0169158#pone.0169158.ref009" target="_blank">9</a>] <b>8.</b> [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0169158#pone.0169158.ref056" target="_blank">56</a>] <b>9.</b> [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0169158#pone.0169158.ref057" target="_blank">57</a>]. All <i>FKBP5</i> transcripts have been collated to show exons (black vertical lines), introns (black horizontal lines) and untranslated regions (black boxes). A transcription factor binding site (TFBS; green box) and DNase hypersensitivity site (purple box) upstream of the top variant are labeled and are not to scale. GRE denotes glucocorticoid receptor response elements (blue boxes) and are not to scale.</p

Haplotype block structures in the <i>FKBP5</i> region.

<p>A collated version of all <i>FKBP5</i> transcripts is represented at the top of the figure. Vertical black lines represent exons, green boxes represent untranslated regions and purple boxes represent intronic regions. The numbered squares display the D’ score, unnumbered squares have a D’ score of 1.0. Three haplotype blocks were generated and are enclosed by black lines. Lines connect the variants to their approximate location within the <i>FKBP5</i> locus.</p

Gene-level results using two minor allele thresholds.

<p>Gene-level results using two minor allele thresholds.</p